Method and equipment for controlling the congestion management and scheduling of transmission-link capacity in packet-switched telecommunications

ABSTRACT

The invention relates to a method and equipment for controlling the congestion management and transmission-link-capacity scheduling in packet-switched telecommunications, in such a way that 1) it is possible to define what share of the capacity of the transmission link will be reserved for traffic representing a specific service level class, and 2) it is possible to define the weighting coefficient that the portion of the traffic exceeding the reservation of each service level class will use to compete for the portion of the capacity of the transmission link that is not reserved, or that is reserved but is not being used momentarily by traffic entitled to the reservation, and 3) it is possible to use overbooking, in such a way that the reduction in service quality due to overbooking affects only the service level class in which overbooking is used, and 4) it is possible to prevent an increase in delays detrimental to traffic-flow control even in a congestion situation arising from overbooking. The invention is based on measuring the traffic flow that comes to be scheduled, in which the flow is formed of packets representing a specific service level class arriving in the queue, or some of the relevant packets, and on controlling the operation of the scheduler and congestion limitation mechanism on the basis of the measurement results.

The present invention relates to a method, according to Claim 1, forcontrolling the congestion management and scheduling oftransmission-link capacity in packet-switched telecommunications.

The invention also relates to equipment, according to Claim 8, forcontrolling the congestion management and scheduling oftransmission-link capacity in packet-switched telecommunications.

In this publication, the following abbreviations are used in thedescriptions of both the prior art and the invention:

-   BE Service level class for applications, which are able to exploit    the momentarily available capacity of a data transmission network,    but for which the capacity of the data transmission network is not    reserved (Best Effort),-   CoS Service level class (Class of Service),-   DSCP Data carried by a packet, stating the service level class to    which the packet in question belongs (Differentiated Services Code    Point),-   FIFO First In First Our discipline,-   aG+E A service level class for applications, which are able to    exploit the momentarily available capacity of a data transmission    network, and for which a specific data transmission capacity is    reserved (Guaranteed rate and Best Effort),-   bG+E A service level class that is similar to aG+E, but, in service    level class bG+E, an overbooking ratio of a different magnitude to    that in service level class aG+E can be used, if desired,-   [P] {p} A variable expressing an internal sub-group (e.g., drop    preference) of a service level class,-   OBR Overbooking Ratio,-   QoS Quality of service,-   q Variable expressing the service level class,-   SFQ Start-time Fair Queuing, one scheduling method [1] based on a    weighting coefficient,-   SLA Service Level Agreement,-   wfq a general term (weighted fair queuing) applied to a scheduling    method based on a weighting coefficient,-   WFQ Weighted Fair Queuing, one scheduling method [1] based on a    weighting coefficient,-   WRED Weighted Random Early Detection, a congestion limitation method    [3, 4] based on a weighting coefficient.

In a packet-switched telecommunications system, it is often preferablefor the packets being transmitted to be classified as belonging todifferent service level classes (CoS), according to the requirements ofthe applications used by the telecommunications service, and, on theother hand, according to the kind of agreements on the service quality(SLA) the telecommunications service provider has made with itscustomers (end users). For example, in the case of normal telephoneapplications, it is essential for the data transmission speed requiredby the application to be available for the time required, for thetransmission delay to be sufficiently small, and the variation in thetransmission delay to be sufficient low. In telephone applications,there is no advantage in being able to momentarily increase the datatransmission speed provided for an application, if the loading on thetelecommunications network is small at the time in question. On theother hand, when downloading web-pages, it is extremely advantageous tobe able to exploit the full, even momentarily available, transmissioncapacity of the network.

It is often advantageous to use overbooking for some service levelclasses. An application representing a specific service level class, forwhich a specific transmission speed [bit/s] is ordered by the servicelevel agreement (SLA), will be examined. The telecommunications networkis required to provide the transmission speed ordered for theapplication in question, with a probability of 99.99%. In order to meetthis demand, the data transmission capacity [bit/s] is reserved in thedata transmission links and other network elements for applicationsusing the service level class in question. When using overbooking, thedata transmission capacity reserved in a specific link or other networkelement is lower than the total sum of the transmission speeds orderedin the service level agreements (SLA) in the case of the relevant partof the network. Overbooking naturally increases the probability ofbreaching the service level agreement (SLA). However, in practice it isimprobable that even nearly all of the end users using the specificservice level class will attempt to simultaneously utilize thetransmission speed defined in their service level agreement. From thepoint of view of the service provider, overbooking is profitable, aslong as the payments from end users received with the aid of overbooking(thus selling more transmission capacity) are greater than the costsincurred by the increase in breaches of the service level agreements.The overbooking ratio (OBR) expresses the ratio of the total sum of thetransmission speeds ordered for specific traffic to the datatransmission capacity reserved for the traffic in question. Theoverbooking ratio can be network element specific.

If overbooking is used in some service level class, it should bearranged so that the overbooking used in the specific service levelclass does not reduce the quality of service in other service levelclasses. Service quality reduction can appear, for example, in the formof increased packet loss, of increased transmission delays and delayvariations, or in a reduced ability of the application to utilize theavailable transmission capacity of the network at any time. The risk ofservice quality reduction caused by overbooking should affect only theservice level class, in which the overbooking is used. In thispublication, overbooking meeting such conditions is termed controlledoverbooking.

The following examines a situation, in which the telecommunicationsservices provides the following types of service level class:

-   -   aG+E (Guaranteed rate and Best Effort) for an application, for        which a service level agreement (SLA) is used to order a        specific (minimum) transmission speed [bit/s] and for which the        momentary data transmission speed provided is increased        exploiting the data transmission system capacity available at        each time. A data transmission capacity [bit/s] is reserved in        the network elements for applications representing the aG+E        service level class.    -   bG+E: a service level class corresponding to aG+E, but in the        service class bG+E it is possible, if desired, to use an        overbooking ratio (OBR_(bG+E)) of a different magnitude to that        in the service level class aG+E (OBR_(aG+E)).    -   BE (Best Effort): for applications, for which a data        transmission capacity is neither reserved in the network        elements, nor, on the other hand, is a (minimum) transmission        speed ordered using a service level agreement (SLA), but for        which the telecommunications system's capacity available at any        time is exploited.

FIG. 1 shows one way according to the prior art of scheduling thecapacity of a common transmission link for traffic flows representingthe aforementioned service level classes (aG+E, bG+E, or BE). Theoperation of the system shown in FIG. 1 is as follows:

-   -   The service level class q, to which an individual packet        belongs, can be identified on the basis of information attached        to the packet (for example, DSCP=Differentiated Services Code        Point [2]).    -   Packets are routed into service-level-specific FIFO queues 3-5        (aG+E, bG+E, and BE queues).    -   Each packet representing an aG+E or bG+E service level class        belongs to an internal sub-group (p) in the service level class,        on the basis of which it is possible to decide at least whether        the packet in question belongs to the portion of the traffic        that corresponds to the minimum transmission speed order in the        service level agreement (SLA), (this will be subsequently        referred to as the G portion), or whether the packet belongs to        the portion of the traffic that exceeds the ordered minimum        transmission speed (this will be subsequently referred to as the        E portion). Membership of a specific sub-group p can be        indicated, for example, with the aid of drop precedence        information carried by the DSCP [2]. The sub-group information        is used when congestion requires a decision to be made as to the        packets in the queue or arriving in the queue on which        congestion limitation measures should be imposed. An example of        this is the WRED method (Weighted Random Early Detection) [3,        4].    -   The capacity of the transmission link is scheduled between the        aG+E, bG+E, and BE queues 5, using a weighting coefficient based        scheduling method (for example SFQ [1]). In a congestion        situation, the capacity of the transmission link is divided        between the aG+E, bG+E, and BE service level classes, in a ratio        determined by the corresponding weighting coefficients        (W_(aG+E): W_(bG+E): W_(BE)).

In the scheduling method shown in FIG. 1, the weighting coefficientsW_(aG+E), W_(bG+E), and W_(BE) are chosen while bearing in mind that thetraffic representing the service level classes aG−E, and bG+E mustreceive the portions of the capacity of the transmission link reservedfor them. A problem in the system shown in FIG. 1 is that, in additionto meeting the aforementioned requirement, it is not possible to definethe weighting coefficient by which the E portions of the trafficrepresenting the service level classes aG+E and b+E and the BE trafficwill compete for the portion of the capacity of the transmission linkthat is not either reserved for the use of traffic representing someservice level class, or is reserved, but is not being used at the momentin question by traffic entitled to the reservation.

FIG. 2 shows a method according to the prior art disclosed in reference[5] (confidential at the time of writing the present application), inwhich the value of the scheduling weight depends on both the qualityclass (q) and the sub-group (p). It is then possible to separatelydefine 1) what relative portion of the capacity of the transmission linkwill be given to the portion of traffic of each service level class thatcorresponds to the ordered minimum transmission speed (the G portions ofaG+E and bG+E) and 2) with what weighting coefficient the trafficportion, which exceeds the ordered minimum transmission speed (the Eportions of aG+E and bG+E and BE), will compete for that portion of thecapacity of the transmission link, which is not at the moment underexamination being used by a traffic portion (the G portions of aG+E andbG+E) representing the minimum transmission speed ordered for someservice level class.

In the system according to FIG. 2, the traffic portions (the G portionsof aG+E and bG+E) entitled to the reservations should be given, on theone hand, sufficiently large scheduling weights relative to thescheduling weights of the traffic portions (BE and the E portions ofaG+E and bG+E) unentitled to the reservations, so that it is possible toensure that the traffic portions entitled to the reservations receivethe use of the transmission capacity portions reserved for them, even ina congestion situation. On the other hand, however, the schedulingweights in questions should be small enough so that the overbooking tobe used in traffic portions entitled to the reservations will reduce theperformance of only the service level class in which overbooking isused. A problem in the system according to FIG. 2 is that it is only inexceptional cases that the said requirements affecting the schedulingweights (ensuring reservations, division of the available transmissioncapacity into the desired ratios, and controlled overbooking) will notbe mutually contradictory.

An additional problem in the methods shown in FIGS. 1 and 2 is that, ina situation in which, for example, the queue 3 of the aG+E quality classhas become congested in the quality class in question due to overbookingbeing used, the congestion limitation mechanism (e.g., WRED [3, 4]) willnot be able to limit the length of the queue in a manner correspondingto that in a situation, in which the congestion is due to trafficrepresenting the E portion being offered. This is because the congestionlimitation mechanism uses sub-group information (e.g., drop precedence)to decide which packets to apply the congestion limitation measures to,when the queue length and/or a variable derived from it exceeds aspecific threshold value. If the sub-group information states that thepacket belongs to the G portion, a higher threshold value is used, whichthe queue length or its derivative must exceed before a congestionlimitation measure is applied to the packet in question, than in asituation in which the packet being examined belongs to the E portion.When using overbooking, the queue can become already congested due tothe effect of only the G portion. Any increase in the length of thequeue will increase the transmission delay and hampers the operation of,for instance, TCP protocol flow control and monitoring mechanisms [6].

The present invention is intended to eliminate the defects of the stateof the art described above and for this purpose create an entirely newtype of method and equipment for scheduling transmission link capacitybetween packet-switched traffic flows. The object of the invention is amethod, by means of which a scheduler and congestion managementmechanism can be implemented, in such a way that the followingproperties are achieved:

-   1) A specific portion of the capacity of the transmission link can    be reserved for traffic representing a specific service level class,    and-   2) it is possible to define the weighting coefficient by which each    portion of the traffic of the service level class, which exceeds the    capacity of the portion of the transmission link reserved for the    service level class in question, will compete for the portion of the    capacity of the transmission link, which is either not reserved for    the use of traffic representing some service level class, or which    is reserved but is not being used at the moment in question by    traffic entitled to the reservation, and-   3) it is possible to use overbooking in such a way that the    reduction in the quality of the service caused by overbooking only    affects the service level class, in which overbooking is used    (controlled overbooking), and-   4) an increase in the queue length that is detrimental in terms of    the traffic-flow control (e.g., using the TCP protocol [6]) can be    prevented even in a congestion situation arising from overbooking.

The invention is based on measuring the traffic flow coming to bescheduled, in which the traffic flow mentioned is formed of packetsarriving in a queue representing a specific service level class, or someof the packets in question, and the operation of the scheduler (e.g.,SFQ [1]) and the congestion-limitation mechanism (e.g., WRED [3, 4]) iscontrolled on the basis of the measurement.

The use of the method according to the invention purely to control thescheduler mechanism does not prevent the use of a traditional congestionlimitation method based on sub-group information (e.g., dropprecedence). Using the method according to the invention purely tocontrol a congestion limitation mechanism does not prevent the use ofscheduling methods according to the prior art.

The measurement result can be a single number, the value of whichexpresses information to be utilized in control, or many number(vector), the values of which express information to be utilized. In thefollowing, the measurement result will be treated as a vector formed ofseveral sub-results, as it is the most general approach.

The method according to the invention is characterized by what is statedin the characterizing portion of Claim 1.

The equipment according to the invention is, in turn, characterized bywhat is stated in the characterizing portion of Claim 8.

The use of the invention achieves the advantage over solutions accordingto the prior art that it is possible to implement the scheduler andcongestion-limitation mechanism in such a way that the reduction inquality arising from overbooking only affects the service level class inwhich overbooking is used and, in addition, can prevent an increase inthe length of the queue that is detrimental to traffic-flow control,even in a congestion situation arising from overbooking.

In the following, the invention is examined in greater detail with theaid of examples according to the accompanying figures.

FIG. 1 shows a block diagram of one system according to the prior art,for scheduling the capacity of a common transmission link for trafficflows representing the aforementioned service level classes (aG+E, bG+E,BE).

FIG. 2 shows a block diagram of a second system according to the priorart, for scheduling the capacity of a common transmission link fortraffic flows representing the aforementioned service level classes.

FIG. 3 shows a block diagram of a system according to the invention, forscheduling the capacity of a common transmission link for traffic flowsrepresenting the aforementioned service level classes.

The theoretical basis of the method according to the invention willbecome apparent from the following examination.

In the weighting-coefficient-based scheduling system, a sequenceindication (for example, Start_tag SFQ in method [1]) is arranged forthe packet in the input to the scheduler 1, to state when the packet inquestion will be in turn for forwarding. The first packet to beforwarded is that with a sequence indication value stating the earliestforwarding moment. The sequence indication need not be bound to realtime, it is sufficient if the sequence indications of the packets are ina sensible relation to each other.

When forming the sequence indication, a weighting coefficientcorresponding to the service level class in question is used for packetscoming from a specific service level queue. If queue J1 has a greaterweighting coefficient than queue J2, then the series of sequenceindications of the consecutive packets of queue J1, relative to those ofthe corresponding ones of queue J2 is formed to be such that the queueJ1 receives a larger portion of the capacity of the output of thescheduler 1.

In the priority-based scheduling system, the packets in the input of thescheduler are given a priority value. The priority values of the packetsdetermine which packet is the next to be forwarded.

In the method according to the invention, the priority value given tothe packet, or the weighting coefficient used in forming the sequenceindication does not depend only on the service level class representedby the packet (which is this publication is referred to as the variableq), but also on the result (which in this publication is referred to asthe variable vector x) provided by the measurement 3 made from thetraffic flow of the service level class in question on from the portionof the traffic flow in question, FIG. 3.

In the method according to the invention, the measurement datum/data canalso determine whether the weighting coefficient or priority-basedscheduling method is used to make the scheduling decision for a specificpacket.

In congestion management, the length of the queue or a variable derivedfrom it, such as a low-pass filtered value, is utilized. If the lengthof the queue and/or its derivative exceeds a specific threshold value,congestion limitation measures are applied to specific packets in thequeue or arriving in it. The congestion limitation measures can bepacket dropping (discarding) or marking (ECN method [2]). The selectionof packets within a specific service level class, to which thecongestion limitation measures are applied, is based on sub-groupinformation (e.g., drop precedence) in a congestion management methodrepresenting the prior art. The principle is that, for example, in thecase of class aG+E, the congestion limitation measures are applied tothe packets representing the service level class in question, which, onthe basis of the sub-group information, belong to the E portion. If theincrease in the length of the queue does not stop by dropping (ormarking) packets representing the E portion, packets representing the Gportion are also begun to be dropped (marked). In the WRED method, thisis implemented in such a way that the threshold value of the queuelength, or the variable derived from it defined for the G portion isgreater than the corresponding threshold value defined for the Eportion. Unless overbooking is being used, the dropping (or marking) ofpurely packets representing the E portion should already preventcongestion, as the necessary transmission capacity has been reserved forthe traffic representing the G portion. If overbooking is used, thequeue can continue to increase even in a situation in which congestionlimitation measures are already being applied to all packetsrepresenting the E portion. This is due to the fact that, when usingoverbooking (as defined), it is possible for a greater amount of trafficrepresenting the G portion, than the transmission capacity reserved forthe G portion to attempt to reach the transmission link. In that case,the length of the queue is limited on the basis of the threshold valuedefined for the G portion. However, in terms of the delay behaviour andflow management (e.g., TCP), it is preferable for the length of thequeue to remain as short as possible. This is attempted, for example,using the WRED algorithm in such a way that the threshold value, afterwhich packets representing the E portion are begun to be dropped (ormarked) is low. On the other hand, a low threshold value cannot be usedfor the G portion, in order to achieve a clear dropping/markinghierarchy-limitation measures are applied first of all to the E portionand only after that to the G portion. Thus, in a congestion situationcaused by overbooking, for example, the basic objective of the WREDalgorithm of keeping the queue short is not met.

In the method according to the invention, the problem described aboverelating to the length of the queue is solved by using measurementresults x, FIG. 3, instead of, or along with the sub-group informationin congestion management.

The following illustrates the operation of the scheduling and congestionmanagement method according to one embodiment of the invention in thecase of traffic flows belonging to the classes aG+E and bG+E, using theSFQ scheduling algorithm [1] and the WRED congestion managementalgorithm [3, 4]. In this embodiment of the invention, thepacket-specific weighting coefficient is defined on the basis of themeasurement results as follows:

For the portion of a traffic flow representing the service level classaG+E, for which, in the case of the packet being examined, the measurednumber of bits transmitted is, during an arbitrary examination period Tfrom the past to the present less than CIR×T+CBS, the packet-specificweighting coefficient W_(aG+E)=W_(ga), for the excess portionW_(aG+E)=W_(Ea). Correspondingly, in the service level class b+E, theweighting coefficient W_(bG+E)=W_(Gb) or W_(Eb). CIR is the availabletransmission band (committed information rate [bit/s]) reserved from theG portion of the service level class, which, when using overbooking isless than the largest possible amount [bit/s] of traffic representingthe G portion. CBS is the largest permitted burst size [bit] (committedburst size). The measurement described here can be implemented using,for example, the Token Bucket method [7].

The portion of traffic formed of packets belonging to the aG+E (bG+E)service level class, for which W_(bG+E)=W_(Ga) (W_(bG+E)=W_(Gb)) isvalid, will subsequently be termed the g portion, and correspondinglythe portion of the traffic formed of packets, for which W_(aG+E)=W_(Ea)(W_(bG+E)=W_(Eb)), will be termed the e portion.

The sequence indications (S_(aG+E)(i) and S_(bG+E)(j)) of an aG+E classpacket i and of a bG+E class packet j are calculated as follows:S _(aG+E)(i)=max{v,S _(aG+E)(i−1)+L(i−1)/W _(aG+E)},  (1)S _(bG+E)(j)=max{v,S _(bG+E)(j−1)+L(j−1)/W _(bG+E)},  (2)in which L(i−1), L(j n−1) are the size of the preceding packet (forexample, in bits) and v is the sequence indication (virtual time) of thepacket being forwarded at the time of inspection. The sequence indictionis calculated when the packet arrives at the quality-level-specificinput of the SFQ mechanism, nor it is updated later, even if v changes.The next packet to be forwarded is selected as the packet (i or j) withthe smaller sequence indication.

A simple test or simulation can be used to demonstrate the following: ifthe packets of service level class aG+E being transmitted during aspecific period of time belong to the g portion of aG+E and the servicelevel class bG+E packets being transmitted belong to the e portion ofbG+E, then the ratio of the bytes (or bits) carried by the aG+E and bG+Eservice level class packets being transmitted during the period inquestion is W_(Ga): W_(Eb). The examination gives a better illustration,if all the packets are assumed to be of the same size. It is thenpossible to speak simple of packets, instead of speaking of packetsrepresenting bits or bytes. By selecting suitable weighting coefficientsW_(Gb), W_(Ea), W_(Gb), W_(Eb), it is possible to define how manypackets representing the g or e portions of the service level class aG+Eare transmitted relative to the packets representing the g or e portionsof the service level class bG+E.

One variation of this embodiment is created in such a way thatW_(Ga)=W_(Gb), W_(Ea)=W_(Eb), and W_(Ga)>>W_(Ea) (W_(Gb)>>W_(Eb)), e.g.,W_(Ga)=10000×W_(Ea). In fact, this corresponds in practice to thepackets belonging to the g portion being scheduling using a priorityprinciple in such a way that the g portions of the service level classesaG+E and bG+E have a mutually equal scheduling priority. This ispossible, because the g portions are limited in such a way that thetransmission band they require is available.

In this embodiment of the invention which is described, the selection ofthe packets inside the service level class aG+E or bG+E, to whichcongestion limitation measures are applied, is not based on sub-groupinformation, but instead of whether the packet being examined belongs tothe g or e portion. The principle is that congestion limitation measuresare applied first of all to packets representing the e portion. If theincrease in the length of the queue does not stop by dropping (ormarking) packets representing the e portion, packets representing the gportion are also begun to be dropped (marked). In the WRED method, thisis implemented in such a way that the threshold value defined for the gportion, which the length of the queue or a derivative of it must exceedbefore packets belonging to the g portion are begun to be dropped (ormarked), is greater than the corresponding threshold value defined forthe e portion.

Because the g portions of the service level classes aG+E and bG+E arelimited in such a way that the transmission band required by them isavailable, the dropping (or marking) of purely the packets representingthe e portions will already prevent congestion. Thus, the length of thequeue in congestion situations is determined by the threshold value setfor the e portion, which can be selected to be low.

One preferred variation of this embodiment is achieved in such a waythat the measuring function is applied only to the G portion and thepackets that do not belong to the G portion are processed in the eportion. Thus, it is possible to ensure that the greatest possible shareof the packet that belong to that portion of the traffic, whichcorresponds to the transmission speed promised in the service levelagreement (G portion), will be processed in the g portion. Theapplication of the measurement to only the G portion can be implementedon the basis of sub-group information (p, e.g., drop precedence).

REFERENCES

-   [1] Pawan Goyal, Harric M. Vin, Haichen Cheng. Start-time Fair    Queuing: A Scheduling Algorithm for Integrated Services Packet    Switching Networks. Technical Report TR-96-02, Department of    Computer Sciences, University of Texas Austin.-   [2] Bruce Davie, Yakov Rekhter. MPLS Technology and Applications.    Academic Press 2000 CA U.S.A. (www.academic.press.com)-   [3] Sally Floyd, Van Jacobson. Random Early Detection Gateways for    Congestion Avoidance. Lawrence Berkeley Laboratory 1993, University    of California.-   [4] A description of the WRED algorithm can be found at the Internet    address:    http://www.jumper.net/techncenter/techpapers/200021-01.html.-   [5] Janne Väänänen. Menetelmä ja Laitteisto Sürtoyhteyskapasiteetin    Vuorottamiseksi Packettikytkentäisten Tietoliikennevoident Kesken    (Method and Equipment for Sequencing Transmission Capacity Between    Packet-Switched Data Traffic Flows), Finnish patent application No.    20021921, Helsinki Finland 2002.-   [6] Douglas E. Corner. Internetworking with TCP/IP, Third Edition.    Prentice Hall International Editions, U.S.A. 1995.-   [7] P. F. Chimento. Standard Token Bucket Terminology.    http://qbone.internet2.edu/bb/Traffic.pdf 2000.

1. A method for controlling the congestion management and the schedulingof transmission link capacity in packet-switched telecommunications, inwhich method digital information is transmitted as constant orvariable-length packets, identifier data is attached to the packets, onthe basis of which the packets are divided into at least two differentservice level classes, on the basis of the service level class data,each packet is routed to one of the FIFO queues, which are one for eachservice level class, at least one service level class is such thatidentifier data is attached to the packets belonging to it, with the aidof which the packets are divided into at least two internal sub-groupsin the service level class, the packets belonging to the same servicelevel class form a flow, in which the transmission order of the packetsis retained, the available capacity of outgoing link or links of asystem is scheduled for the service-level-class-specific FIFO queuesusing a weighting-coefficient-based scheduling method, a priority-basedscheduling method, or a combination of these methods, and congestion inthe service-level-class-specific FIFO queues is limited by dropping ormarking packets in the queue or arriving in the queue, wherein apacket-specific priority value in the priority-based scheduling and/or aweighting coefficient in the weighting-coefficient-based scheduling isdefined from a joint effect of a variable q and a variable vector x andthat a selection of packets within a specific service level class, towhich packets dropping or marking will be applied in a congestionsituation, are defined from an effect of the variable vector x, in whichthe variable q is defined from the service level class, to which thetraffic represented by the packet in question belongs, and the variablevector x is formed of the results provided by measurement applied to thetraffic flow representing the service level class being examined, saidmeasurement results depending on temporal variation in data transmissionspeed of the traffic representing the traffic flow being examined and ondistribution between different sub-groups of packets representing thetraffic flow being examined.
 2. The method according to claim 1, whereinthe temporal variation in the data transmission speed is depicted usinga double-value variable, which states whether the number of bitstransmitted during an arbitrary monitoring interval T from the past tothe present is less than CIR×T+CBS, in which CIR is the transmissionband available to the service level class being examined (committedinformation rate) and CBS is the greatest permitted burst size(committed burst size).
 3. The method according to claim 1, wherein theSFQ (Start-time Fair Queuing [1]) method is used as theweighting-coefficient-based scheduling method.
 4. The method accordingto claim 1, wherein the WFQ (Weighted Fair Queuing [1]) method is usedas the weighting-coefficient-based scheduling method.
 5. The methodaccording to claim 1, wherein the WRED (Weighted Random Early Detection[3, 4]) method is used as the congestion limitation method controlled bythe variable vector x.
 6. The method according to claim 1, wherein theinformation contained in the variable vector x is formed using the TokenBucket method [7].
 7. Equipment for controlling the congestionmanagement and scheduling of transmission link capacity inpacket-switched telecommunications, in which the equipment includesmeans for receiving constant or variable-length packets carrying digitalinformation, means for reading the identifier data attached to thepackets, on the basis of which the packets can be divided into at leasttwo different service level classes, means for dividing the packets intoat least two different service level classes, a FIFO queue for each ofthe service level classes, means for routing a packet in the FIFO queuecorresponding the relevant service level class, on the basis of theservice level class data, means for reading identifier data attached tothe packets, on the basis of which the internal sub-group of the servicelevel class, to which the packet in question belongs, can be determined,a scheduler for scheduling the available capacity of outgoing link orlinks from a system to the service-level-class-specific FIFO queues,using a weighting-coefficient-based scheduling method, a priority-basedscheduling method, or a combination of these, means for sending packetsto the outgoing link or links, in a transmission order defined by thescheduler, and means for limiting the congestion of theservice-level-class-specific FIFO queues, by dropping or marking packetin a queue or arriving in a queue, wherein the equipment includes means,with the aid of which a packet-specific priority value can be defined inthe priority-based scheduling and/or a weighting coefficient can bedefined in the weighting-coefficient-based scheduling on a basis of ajoint effect of a variable q and a variable vector x, and with the aidof which means selection of packets within the service level class, towhich packets dropping or marking is applied in a congestion situation,can be defined from an effect of the variable vector x, in which thevariable q is defined from a service level class, to which the trafficrepresented by the packet in question belongs, and the variable vector xis formed of the results provided by measurement applied to the trafficflow representing the service level class being examined, saidmeasurement results depending on temporal variation in data transmissionspeed of the traffic representing the traffic flow being examined and ondistribution between different sub-groups of the packets representingtraffic flow being examined.
 8. The equipment according to claim 7,wherein the equipment includes means, with the aid of which adouble-value variable can be formed, which states whether the number ofbits transmitted during an arbitrary monitoring interval T from the pastto the present is less than CIR×T+CBS, in which CIR is the transmissionband available to the service level class being examined (committedinformation rate) and CBS is the greatest permitted burst size(committed burst size).
 9. The equipment according to claim 7, whereinthe equipment includes means for performing weighting-coefficient-basedscheduling using the SFQ (Start-time Fair Queuing [1]) method.
 10. Theequipment according to claim 7, wherein the equipment includes means forperforming weighting-coefficient-based scheduling using the WFQ(Weighted Fair Queuing [1]) method.
 11. The equipment according to claim7, wherein the equipment includes means, with the aid of whichcongestion limitation controlled using the variable vector x can beperformed using the WRED (Weighted Random Early Detection [3, 4])method.
 12. The equipment according to claim 7, wherein the equipmentincludes means for forming the information contained in the variablevector x using the Token Bucket method [7].